In a direct-online synchronous reluctance motor (DOL SynRM) small air-gaps may be added between an outer rim of the rotor and a cage structure. This design allows the rotor to operate a little cooler during a variable speed drive (VSD) testing which supports the theory that small air-gaps prevent harmonics to flow through the cage during a steady state operation.
However, bridges through apertures of the stack elements result in loss on a power factor (PF) and complicate the mask plate structure. For an induction motor (IM), the losses caused by the VSD harmonics, which are harmonic electric currents flowing at the top parts of the rotor, are a well-known phenomenon which wastes energy and rises the temperature of the rotor. Hence, there is a need to improve the rotor.